Most people over 30 don’t have many (or any) business or personal relationships that don’t involve communicating by email. There are very few people who matter to me with whom I do not regularly communicate by email. Nearly every causal business relationship becomes more substantive through email communication. The only communication platform everyone in my family shares is email.

What’s interesting when you think about email as the social graph is that there is a much higher relationship threshold for email. I’ve been added as a “friend” on Facebook by people I’ve never met, don’t know, and have never communicated with. Same with LinkedIn. It’s way to easy to “add” someone on a social networking application. Just click a button.

Sending someone an email, in contrast, actually requires having something to say. It requires introducing yourself. It requires actually COMMUNICATING substantively, rather than just empty gestures like adding, poking or sending virtual beer.

Want more evidence that, far from being dead, email is the adult social graph? Check out the most recent quarterly earnings report for RIM, who makes the Blackberry. Revenue rose year-over-year to $1.67 billion from $835.1 million. From what? Selling EMAIL devices.

So what about for people under 30? Over the holiday, I did some ethnographic research with various family members between the ages of 17 and 23. As expected, they check email infrequently, because they are still in school and haven’t yet had a business email and its obligations thrust upon them.

What’s interesting is that they don’t us IM much either, nor do they use Facebook or MySpace much. So what do they do? They text each other on their phones.

And, get this…they call each other and actually TALK. Can you believe it? Social networking through actual direct human communication.

Unlike most people in the business world, students aren’t in front of their computers all day long. Their cell phones are their main computing devices. So their social graph is their cell phone contact list. The people they text and call.

I saw these young adults away from their computers all day without concern, but they were checking their cellphones constantly. The same way older demographics check their Blackberries.

It seema that we are increasingly inclined to take our social graphs with us — but not through web-based social networking applications.

I spent a lot of time with non-geeks over the holidays, and while I heard mention of email, texting, and cellphones in casual conversation over many days, I didn’t hear a single mention of Facebook, MySpace, or any other web-based social networking application.

If you prefer numbers over anecdotal evidence, just following the money — consider: Why is RIM so profitable? Why do people pay so much money for cell phone service and text messages? Why is there so much money in email spam?

Facebook’s $15 billion valuation suggests that that dollars are about to flow into the social graphs based on proprietary web applications. Would you bet on that, or an open social platforms like email, SMS, and….phone numbers?